1. Field of the Invention
It is well known that various metallic elements are found in petroleum crude oils. A list of those that may be present are set forth in U.S. Pat. No. 2,910,434. The most common are iron, nickel and vanadium. These metals, particularly iron, nickel and vanadium, are harmful when included in feedstocks used for further refining operations. For example, in hydrocracking operations the plating out of iron metals on the catalyst's exterior surfaces can over a time cause interstitial plugging of the catalyst bed. This limits the catalyst life in a hydrocracker since unacceptable pressure drops develop. Additionally, the metalliferous deposits serve to deactivate (poison) the catalyst requiring premature shutdown of the reactor and replacement of the catalyst. Conventional catalysts having surfaces areas typically ranging from 100 m.sup.2 /gram to as much as 400 m.sup.2 /gram and having relatively small pore diameters are quite active for removing metals from hydrocarbons. However, they are particularly susceptible to interstitial plugging as well as being economically unattractive for removal of metal contaminants. The process of the subject invention uses a catalyst which surprisingly combines low surface area and large pore size with effective removal of metal contaminants with reduced interstitial plugging of the catalyst bed.
2. Description of the Prior Art
U.S. Pat. NO. 2,910,434 teaches the removal of trace metals from a cat cracking feed by contacting the feed with hydrogen and an inert packing material.
U.S. Pat. No. 2,985,582 teaches the use of "large surface" materials which may be porous to pretreat feedstocks for removal of ash.
U.S. Pat. No. 3,073,777 teaches the removal of inorganics from crude oils by use of large surface materials.
U.S. Pat. No. 3,340,180 teaches the use of catlyst with pores ranging up to 300 A for hydrodesulfurization of a feed containing asphaltic and metalliferous compounds.
U.S. Pat. No. 3,530,066 teaches preliminarily treating the feedstock to the hydrotreating zone with a particulate solid having pores in the range of from 1,000 to 50,000 A containing a metal component and an alumina hydrogel to remove metals and asphaltenes.
U.S. Pat. No. 3,365,389 teaches the use of a guard bed of silica, alumina, etc., without a hydrogenation component.
U.S. Pat. No. 3,362,901 teaches removal of asphaltenes over an inert particulate support containing a Group VIII iron transition series metal or the use of the inert material alone.
U.S. Pat. No. 3,640,817 teaches the use of a catalyst wherein 50 percent of the pores have an average pore diameter of 1,000 A or greater effective for the removal of asphaltenes.